1. Field of the Invention
The present invention relates to wind and water powered energy harvesters, in particular Magnus type power generators.
2. Description of the Related Art
Although, Savonius turbines have previously been used as effective fluid (e.g. wind, water) motion power generators, this design has the drawback that the Savonius turbine cannot rotate faster than speed of the moving fluid. As a result, Savonius turbines are not suitable for high power generation, and are generally used only in applications where low power generation capability is acceptable.
By contrast, alternative turbine designs, such as propeller type designs, can provide high power generation capability, at least in higher wind speed situations, but such propeller designs often operate with low efficiency when wind speed is low.
Other types of fluid motion power generators are also known. For example, Magnus type power generators. Magnus power generators utilize the Magnus force or “lift” that is generated when one or more fixed (relative to a horizontal rotary shaft) but rotating cylinders rotate in a moving fluid environment. The Magnus force operates in a direction perpendicular to the axis of rotation of the cylinder, and because many prior art Magnus forces used the rotating cylinders in a fluid environment where the axis of rotation of the cylinder was horizontal, and the fluid movement was also horizontal but generally perpendicular to the axis of rotation of the cylinder, the resulting force direction was often in a vertical or “up” direction, and thus the term Magnus “lift” is often used to refer to this Magnus force, even when the actual direction of the force is not always in an upward direction.
This Magnus force or lift can be used, for example, to rotate a horizontal rotary shaft, which in turn can be harnessed to do useful work, such as electrical power generation.
Prior art on such Magnus type power generation methods and devices includes U.S. Pat. No. 4,366,386; U.S. Pat. Nos. 4,717,832; U.S. Pat. No. 4,582,013; U.S. Pat No. 5,074,710; and U.S. Pat No. 5,222,833; the disclosures of which are incorporated herein by reference.
U.S. Pat. No. 7,504,740 to Murakami et. al. describes a Magnus type wind power generator that includes a horizontal rotary shaft for transmitting torque to a windmill-like power generating mechanism. Here the Magnus rotary cylinders are disposed radially on a horizontal rotary shaft. Driving motors rotatively drive the respective Magnus rotary cylinders around the main axes of the Magnus cylinders. The relative action between rotation of each Magnus rotary cylinder, and the wind, produces Magnus forces perpendicular to the axis of rotation of the various rotating Magnus force cylinders. These cylinders in turn rotate the horizontal rotary shaft, which in turn is coupled to an electrical power generating mechanism such as an electrical generator. The invention also teaches an air flow device that may be used to increase the Magnus lifting force, which may be installed on the outer peripheral surfaces of the rotary cylinders.
A similar design was also taught by Ito et. al. in “A study on Savonius Type Magnus Wind Turbine” Ewec 2007 proceedings.info, 2007.